Conjure Shield

You cause a shimmering, translucent magical shield to apparate on one of your arms that is not holding a weapon or shield. This shield gives you a +2 bonus to your armor class and does not require proficiency in shields to use effectively.

The shield hovers just in front of your forearm, so it does not require you having a free hand to hold it, however the spell ends early if you hold a weapon or shield in the same hand that the shield is protecting.